It is common in the field of medicine to perform visual examination to diagnose disease. For example, visual examination of the cervix can discern areas where there is a suspicion of pathology. However, direct visual observation alone may be inadequate for proper identification of an abnormal tissue sample, particularly in the early stages of disease.
In some procedures, such as colposcopic examinations, a chemical agent, such as acetic acid, is applied to enhance the differences in appearance between normal and pathological tissue. Such acetowhitening techniques may aid a colposcopist in the determination of areas in which there is a suspicion of pathology.
Optical analysis has increasingly been used to diagnose disease in tissue. Optical analysis is based on the principle that the intensity of light that is transmitted from an illuminated tissue sample may indicate the state of health of the tissue. As in colposcopic examination, optical analysis of tissue may be conducted using a contrast agent such as acetic acid. The contrast agent is used to enhance differences in the light that is transmitted from normal and pathological tissues.
Optical analysis offers the prospect of at least partially-automated diagnosis of tissue using optical data obtained from the tissue. However, current focusing methods generally do not provide sufficiently accurate levels of focus for acquiring diagnostic optical data from a tissue sample. High quality focus is necessary to provide data with sufficiently low noise. Tissue surface roughness, as well as obstructions such as glare, shadow, and blood, make achieving adequate focus difficult.
Even where adequate focus levels may be achieved, current focusing methods are generally not fast enough to allow acquisition of diagnostically-relevant optical data. Focusing speed is important, for example, in optical analysis of an acetowhitening examination, since spectral data must be obtained within a finite period of time following application of acetic acid to the tissue. Furthermore, current focusing techniques are not sufficiently robust such that consistent focus levels are achieved over the lifetime of the optical instrument.
Thus, there exists a need to improve focusing accuracy, speed, and robustness in optical systems that acquire diagnostic optical data.